I have done this trip 5 times going back to the late 70's and as recently as 2003 with my wife and two kids. A great companion book for the trip is John Wesley Powell's "The Exploration of the Colorado River and Its Canyons." I highly recommend Moki Mac Outfitters in G.R. for rentals and shuttling. They've been around since the 60's and are reasonable and reliable. Here's a photo my now-wife and I at Trin Alcove 30 years ago. http://www.summitpost.org/labyrinth-canyon-ut-circa-1981/599631

Canoed down this section of the river with another couple. We both had 5 month old kids that were only a day apart in age. Canoe camping with kids sure beats backpacking where you have to carry the little boogers the whole way. We did the trip in only 3 days, next time we will take at least twice as long when the kids are a little older and are ready to hike some of the fantastic side canyons.